Would a time traveller start a pandemic?

Or would they die of diseases their immune system couldn't protect against?
02 June 2023


An egg timer showing time running out



Gary wrote in to ask, 'Suppose I build a time machine that can transport me one decade, one century or one millennium into the past or future. Would I, with all my typical 2023 bacteria, viruses, antigens, etc., landing in an urban setting, become the starting point for an epidemic? Or would I quickly die to pathogens that are not common today?'


Joining James Tytko to help answer this question was Brian Ferguson, University of Cambridge Immunologist.

Brian - It’s a great question, Gary. I would have thought going forwards in time will likely have little impact on others, as you are unlikely to be right now carrying a pathogen that is untreatable in the future owing to better healthcare. If you were to go back in time to somewhere prior to 1940, however, you might well be the cause of an outbreak, as long as you assume you end up in a densely populated urban area. This is because the people you will meet are likely not immune to one or more of the pathogens you are carrying now (for example, flu, Sars, rhinovirus etc..).

James - Think about the impact of the Eurasian infections which had a devastating impact on Native American people during the colonial period, wiping out 90% of the population. But what about the impact on the time travelling individual themselves, Brian?

Brian - Well, if you go forward in time far enough, it’s also possible you will catch a disease that has not yet jumped into humans but is circulating in the population at the exact time you ‘land’, although you would probably have to be quite unlucky for this to happen. Similarly, if you go back far enough (more than 100 years, say) you may be unlucky enough to catch and die of smallpox as you are likely not vaccinated against it.

James - This is all assuming our traveller is up to date on all the jabs we’re provided by modern medicine?

Brian - Exactly. If you remove medicine as a variable, and you assume no one is vaccinated against anything and there are no hospitals, then all bets are off. In this hypothetical scenario, you will likely suffer badly from something nasty you catch when you land and you may well spread something you are currently carrying into an immune naïve population. You would be the time-travelling version of patient zero.

James - There you have it Gary - with great power comes great responsibility.


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